The National Weather Service says people could suffer heat exhaustion across the eastern half of San Diego County Friday and Saturday unless they take steps to cope with temperatures that will hit the upper 90s in many inland valleys and foothills and 115 to 120 degrees in the low deserts.

An excessive heat advisory will go into effect at 8 a.m. on Friday as the worst of the heat wave gets underway. But the uncomfortable and potentially unhealthy weather has already started. Temperatures hit 90 and above in many areas of the county Wednesday, including Escondido, Alpine, Ramona and Campo. It was 108 in Borrego Springs and 105 in Ocotillo Wells. The heat will edge higher Thursday, then rise significantly on Friday as a high pressure system deepens over the western U.S.

The weather service says in an advisory, "Exceedingly high temperatures can cause heat-related illness or death. Those working or playing outdoors, and those without air conditioning are most vulnerable ... Take extra precautions if you work or spend time outside. When possible, reschedule strenuous activities to early morning or evening. Know the signs and symptoms of heat exhaustion and heat stroke. Wear light weight and loose fitting clothing when possible, and drinking plenty of water."

There's one bit of good news: The monsoon isn't expected to flow into the county, which reduces the risk of wildfires.

Shore thing: Solspot.com says a modest south swell will produce waves in the 3' to 5' range in North County on Thursday and Friday, and 3' to 4' waves in South County. Stand-out spots include Oceanside. Sea surface temperatures: 67-71.